1. Field of the Invention
The present invention relates to a wireless communication system including fixed and mobile wireless terminals that connect to base station apparatuses.
2. Description of the Related Art:
In a WiMAX (Worldwide Interoperability for Microwave Access) system that enables communications in various places by covering communication areas by multiple base station apparatuses, wireless terminals establish a session through a base station apparatus to perform communication. By establishing sessions, communications having a guaranteed quality can be continuously performed.
However, a wireless terminal in the WiMAX system can move out of the coverage area of a base station apparatus. If a wireless terminal which has established a session moves out of the coverage area of the base station and becomes and remains unreachable for some time, the wireless terminal autonomously disconnects the call but information about the session remains in the WiMAX system. It is disadvantageous for session management and band management if information about a session that is no longer used for communication remains in the system. Therefore it is necessary to clear out residual session information.
A known typical method for clearing out a residual session is to forcibly disconnect the session in which no communication has been performed for a period longer than or equal to a predetermined time period (see Japanese Patent Laid-Open No. 2002-330489 or No. 2008-28996). By using the technique, session information remaining in a system can be cleared from the system.
On the other hand, depending on the nature of an application used, no communication may be performed for a long period of time under normal conditions. The technique disclosed in Japanese Patent Laid-Open No. 2002-330489 or No. 2008-28996 can disconnect a session in which no communication has been performed for a long period of time under normal conditions. This is a problem for an application, for example, that runs based on the precondition that the session will continue. There is a technique that sends data for maintaining a session to prevent forced disconnection of the session (see Japanese Patent Laid-Open No. 2006-195690).
Mobile wireless terminals (hereinafter referred to as “mobile terminals”) and fixed wireless terminals (hereinafter referred to as “fixed terminals”) coexist in a WiMAX system. Terminals that move out of the coverage of a base station apparatus while maintaining a session are mainly mobile terminals and fixed terminals are less likely to exit from the coverage of a base station terminal.
If any sessions, during which no communication has been performed for a predetermined time period or longer, are forcibly disconnected regardless of whether the terminals are fixed or are mobile terminals, most residual sessions of mobile terminals can be cleared out but sessions of fixed terminals during which no communication has been performed under normal conditions in most cases will be disconnected. Consequently, for a fixed terminal that is in the on state in the nighttime, for example, disconnection from and reentry into a session are repeated, which can squeeze the system bandwidth and place an extra load on an authentication server.
On the other hand, if every wireless terminal sends data for maintaining a session in order to prevent forced disconnection of the session, the traffic on the network will increase.